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1,475,201 J. F. TOOMEY TELEPHONE EXCHANGE SYSTEM Filed Dec. 18. 1920 2 Sheets-Sheet 1 R J :71 3 r Ma L H m w w mo m m IEW W0 H Z M 1 H .1 A m TC W 7 1| fi a m 2 F Z 2 l m J u m 1. an 1 NR C05 4 L l W i m: gm. W M Ma Mm/L 6 B 4 W n3 5OURCE\ 0 m w H W w m -On-unun-n-c WI- unnpnumv Patented Nov. 27, 1923.

UNITED STATES PATENT OFFICE.

JOHN F. TOOMEY, 0F NEvll' YORK, N. ASSIGNOR T9 AMERICAN TELEPHdNE AND TELEGRAPH COMPANY, A COEPURAT ON (BF Il'EVJ YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed December 18, 1820. Serial No. 431,704.

To all whom it may concern:

Be it known that I, JoriN l1. Toosiny, residing at New York, in the county of New York and State of New Yorlchaveinvented certain lm n-ovements in lelephoneExchange Systems, of which the following is a specification.

This invention relates to a telephone ex change system and more particularly to a system in which toll connections are estalr lishcd between exchanges by means of machine switching equipn'ientcontrolled over the toll lines.

Under the present practice followed in connection with one system of this nature the subscriber in one exchange desiring a connection with a subscriber in a distant exchange, first obtains a connection with a toll o erator in his own exchange who then ex tends the connection over a to l line and rings up the toll operator at such exchange. The toll operator at the distant exchange upon answering, requests of the originrnting toll operator the number of the desired line and then extends the connection over a switching trunk to the position of a terminating operator in the desired local oiiice of the distant exchange which latter operator then proceeds to extend the connection to the desired line.

This method of extending toll connections may be simplified. by eliminating the services of the incoming toll and terminating operators at the distant exchange. This zuecomplished by terminating the toll lines in automatic selector switches in such a manner that the toll operator at the origin" i exchange can. obtain a connection wit desired subscribefs line ate. distant exchange without the assistance of other toll operators. By' the use of automatic s witches it is not only possible to etlect economy, due tothe elimination of the distant subscribers lines in the distant exchange,

the toll lino holding time is reduced and the service materially improved.

Toll lines, unless emplqvod to their full the capacity for speech and Morse transmission channels, are unprofitable to maintain. It is therefore desirable when adapting such toll lines for automatic operation to tollow manual. practice and permit operation over such lines in both directions while still main taining the toll lines as ei'iicient Morse channels. To accomplish this desired end it is proposed to associate automatic switching mechanism with each end of each toll line and to control the mechanism at each end over the toll line from the other end thereof by directive impulses of alternatingcurrent. The employment of alternating cur rent for controlling the switching mecha nism, not only affords more etficient trans.

mission, but also permits the use of the con ductors of tie toll-line as direct current Morse channels without interference therewith. It is further proposed to supervise the establishment of such a connection by the employment of the line as: a duplex chan nel over which supervisory signals oi alternating current may be sent simultaneously in both directions. Each toll line there fore is a self-contained unit which may be employed for the establishment of connections in either- .tiirection It is therefore an object or" this invention to provide an improved means for directly establishing; a connection from a toll line to a subscribers line by means of automatic switching mechanism.

Further objects at this invention are to control automatic switching mechanism and the supervision ot connections in either direction over a toll line by means of currents oi 5-. selected frequency witl'iout inter 'eringg with the eiiicieucy of the toll line for speech transmission or the employment of the toll line for the transmission of Morse signals.

A feature oi the invention is to selectively operate thermionic devices in accordance with the strength of current supplied thereto.

These and other objects: of the invention will be more readily understood by reference to the accompanying drawings in which Fig. 1 shows the outgoing end of a toll line which is provided with an outgoing calling branch terminating in a jack, and an incoming called branch terminating in auto matic switch mechanism, together with the apparatus necessary to control the trans-- mission and reception of switch controlling and supervisory impulses, and the calling' end of an originating toll operators cord circuit; and Fig. 2 shows circuits similar to those of Fig. 1, located at the incoming end of the toll line.

In general the system functions in the following manner:

A subscriber in the exchange X, Fig. 1 desiring a connection with a subscriber in the exchange Y, Fig. 2, which exchange may be reached directly from exchange X over the toll line L, first obtains a connection through the position ot the usual it or answering operator, *itn the toll operator. A l ter receiving instructions from the calling subscriber through the A operators position, the toll operator reaches the calling subscribers line over a toll swi 'ching trunk by means of the cord O, and extends the connection by means of the calling plug of her cord circuit to an idle toll line extending to the desired distant exchange Y. In response to the seizure of the toll line, alternating current of cycles frequency is connected to the toll line at the outgoing end thereof and causes the toll line to be cut through to the first selector switch in which the toll line terminates at the distant exchange. Following the cutting through of the toll line, current of 135 cycles frequency is connected to the toll line at its incoming end for operating a supervisory signal associated with the originating toll operators cord circuit for giving the toll operator a dialing signal. The operator then proceeds to transmit switch controlling impulses over the toll line by interrupting the flow of the 135 cycle current which current was connected to the toll line at the time the toll line was taken "for use.

In response to the switch controlling impulses the automatic switching mechanism at the exchange Y is operated to select the terminals 0? the desired line After dialing the number ol the desired line ii. the toll operator disconnects the dial 'tlOili her cord circuit and throws the ringing key of the cord circuit to apply ringing current to the outgoing terminals oi the toll line. The application oi ringing current to the outgoing terminals of the. toll lie causes the strength ot the 135 cycle current flowing over the toll line to be increased whereby meclntnism is OPGIfltGt at the incoming end of the toll line for applying ringing current to the line of the called subscriber. Upon the response of the called subscriber. the 135 cycle current which up to this time has been flowing over the toll line from the distant exchange to the originating exchange is cutoff, thereby causing the supervisory signal at the cord circuit oi, the toll ope 'ator to be extinguished to signify to the toll. operator that the called subscriber has responded.

Upon the termination of the conversation and the restoration of the receiver at the substation of the called subscriber in the distant exchange Y. the 135 cycle current is again connected to the toll line at the incoming end thereof and the supervisory signal at the originating toll operators cord circuit is again lighted to indicate to the operator that the connection is no longer needed and may be restored. lVhen the originating operator withdraws the plug of her cord circuit "from the jack of the toll line. cycle current is withdrawn from the toll line at the outgoing end thereof and the apparains at the incoming end which was employed in the establishment of the connection is restored.

As the toll line is adapted for use as a two-way trunk the apparatus at the two ends of the toll line is identical. To simplify the drawings only the apparatus necessary for establishing a connection from the exchange X to the line of a suiscriber in the distant exchange Y has been disclosed in full. At theexchanges X and Y the calling end only or the toll operators cord circuits 0 and 0 have been disclosed since the invention is not concerned with the manner in which connections are established between calling lines and the cord circuits of the toll operators positions. At th exchange Y only such portions of the circuits of the connector switch 250 have been disclosed as are deemed necessary to disclose the invention, it being understood that any well known connector switch of the step-by-sten type may be employed. At the exchange A: the selector switch and the connector switch 150, corresponding respectirely to selector switch 200 and connector switch 25?) of exchange Y, have been diagrammatically represented by the respective wipers ot' the switches.

The toll line is branched at each end, one branch being provided with a high pass filter which is so arranged as to attenuate and practically extinguish current of i553 cycles frequency and to transmit without at tenuation current oi voice frequenz y. These i'ilters are represented by rect. es labeled ligh. pass lilter and may be of the type disclosed in the patent to Usborne 1,3 827. issued September 2. 1919. The other branch of the toll line is tuned to respond only to current. having a frequency of 185 cycles. This tuning is provided by apparatus which has been disclosed in the drawing as ineluded within the small rectangles labeled Tuned circuit and may be 01" the type disclosed in the patent to Stone 729,10el. issuer May 2", 1903. The 135 cycle current incoming to either end oi the toll line through the lranches of the toll line provided with the tuned circuit above described. is received by a pair of thermionic relays oi the audion lllll llll type, one of these thermionic relays being responsive only to current of increased strength. These thermionic relays each control an alternating current relay which is COIH'LBCtGd to the output circuit of the respective thermionic relay.

Having now outlined in a general manner the operation of the system and de scribed brleily the nature of the apparatus employed it is believed that clearer undcrstanding ot the invention may be had from the following detailed description of the method of extending a connection from the line of a subscriber in the exchange X to the line of the subscriber B in the exchange Y, it being assumed that the directory number oi? subscriber B is 256. The subscriber in the exchange X upon initiating the call, lights the line signal before the answering or A. operator, which operator answers the call and upon ascertaining from the calling subscriber that a toll connection is desired extends the connection from the line of the calling subscriber to the toll operators position. The toll operator answers the call in the usual manner and receives instructions from the calling subscriber tor further extending the connection. The toll operator then secures a connection with the calling line over a toll switching trunk in the usual manner.

it will be assumed in this case that the toll operator employs an idle cord circuit 0 at her position, the calling end only of this cord circuit being disclosed in Fig. 1 of the drawing. The toll operator selects an idle toil trunk line extending to the exchange Y, the busy trunk lines of the group extend ing to this exchange being marked by the busy battery potential upon the sleeves of the jacks of these trunk lines and also by drop signals 101 which are operated when therespective trunk lines are busy. It Wlll be assumed that the trunk line L disclosed in the drawing is idle and that therefore the operator inserts the plug l of the cord circuit into jacl: J of this trunk line. A. circuit thereupon established extending from grounded battery through the normally closed make contacts of the dialing key 102, the winning of marginal supervisory relay 108, the winding oi": the slowto-release relay 104-, sleeye contact 105 of the plug P, sleeve contact 106 of the jack J, the left-hand armature and back contact of sl()wdo-i'eleasc relay 107, the winding of slow-to-release relay 108, the winding 01 impulse relay 109 and thence to ground through the resistance element 110. Relays 10-1, 108 and 109 are energized in this circuit but relay 10. being marginally wound does not receive sutlicient current at this time to energize.

The energization of relay 10d establishes the continuity of the tip strand ot' the operators cord circuit 0. The energization of relay 10b is without effect at th s time except that the opening of its left-hand normal contact; interrupts the connection between the ring conductor of the trunk and the inner contact of relay 131 thus cltec tively disconnecting the automatic apparatus at exchange X from the trunk. ielay 109 upon energizing connects the source 111 of 135 cycle alternating current to the primary transmitting winding 112 of the circuit 113 over a circuit which may be traced from one terminal of the source 111 through the outer armature and front contact ot' relay 109, conductor 114-, primary winding 112, conductor 115, resistance element 11.6 and. thence through the inner arnmture and front contact of relay 109 to the other terminal ot the source 111. Since resistance element 116 is included in the circuit above traced the current from the source 111 will not be transmitted through the primary winding 112 at its full strength. Current flowing through the primary transmitting winding 112 induces current into the sec ondary transmitting windings 117 or the circuit 113 and thence to the conductors if the toll line L through the tuned circuit 118 to the grid and filament of thermionic relay 201. This circuit be traced from the grid of the thermionic relay 201 at the change Y over conductor 202, through the upper left-hand coil of the secondary winding 203 of the circuit 204, through the tuned circuit 205, conductor 206 of the toll line L, through the tuned circuit 118 at the exchange X, thence through the upper coils of the secondary winding 11?, through the balancing network 119, thence through the lower coils of the secondary Winding 117, through the tuned circuit 118, conductor 207 of the toll line L, through. the tuned circuit 205 at the exchange Y, thence through the lower lefthand coil of the secondary winding 203, conductor 203 to the filament ot the thermionic relay 201. A circuit in parallel with portion ot the circuit above traced esdend from the grid Ot-the thermionic relay 209 to the conductor 202, and trom the filament of the thermionic relay 209 to the conductor 208. It is to be noted that current flow ing in the circuit 118 at the exchange X and impressed thereon from the primary winding 112 has no etlect upon the thermionic relays 120 and 1.21.

The thermionic relay 201 responds to the current received in its input circuit, but thermionic relay 209 being marginal. does not respond to the weakened current transmitted from the source 111 through resistance 116. Thermionic relay 201 upon responding causes an alternating current to flow in its output circuit, which extends from the plate of relay 201 through condenser 212 and the alternating current relay 213 to ground. The B battery 211 upplies a constant potential to the plate of relay 201 through the impedance coil 210.

Relay 213 is now energized and at its armature end :tront contact closes a circuit extending in parallel. through the windings 0t relays 21-1- and 275, which circuit may traced from grounded battery through the winding of slowto-release relay 21-1, con doctor 215, the armature and back contact of Slow-to-release relay 216, conductor 217, and thence to ground at the armature and "front contact or" relay 213. The circuit of relay 275 may be traced from grounded batter through the winding o'if this relay, conductor 21" thence over conductor 215 and to ground as previously traced at the armature and front contact of relay 213. Relay 21 1 is energized and at its right-hand armature and front contact opens the circuit normally extending from the sleeve 218 of jack J through the windings of relays 216 and 219 tor preventing the toll operator at the exchange Y from operating these relays to initiatc a call. At its right-hand armature and front contact relay 21-1 connects grounded battery through the resistince element 220 to the sleeve 218 of the jack J" "for marking the jack 01'' the toll line L with busy poten tial so that the toll operator at the exchange Y upon testing the jack of this tell line will know that the toll line is in use. it its inner le'l t-hand armature and front contact relay 21 1 establishes a circuit for the drop which may be traced from grounded battery through the inner left-hand armature and front contact of relay 21 1 and thence to ground through the winding of drop 221. The operation ot' drop 221 serves to Further signify that the toll line L is in use.

Relay upon energizing opens its right-hand armature and back contact the circuit extending over conductor 222, conductor 223 and through the winding of relay 2241: for preventing a "false operation oi? relay 221 at this time. At its lett-hand armature and trout contact relay 27:") establishes a circuit through the windings of polarized supervisory relay 225 and the windings of line relay 220 01 the selector si t-h 200. The circuit oi relay 220 may be traced from grounded battery through the left-hand winding of relay 22 the outer left-hand armature and back contact. of switching relay 223, conductor 229, the windings of polarized supervisory relay 225, the lefthand armature and front contact of relay 275, conduct-or 230, the inner left-hand armature and back contact 01? relay 22S and thence to ground through the right-hand winding of relay 2G. Relays and 225 one 'gize in this circuit, relay 226 closing at its armature and front contact a circuit for the slow-to-release relay 231 which in turn at its right-hand armature and "trout contact prepares a circuit through the primary stepping magnet 232 of the selector switch 200.

The current flowing through the windings of polarized relay 225 is now in such a direction as to cause this relay to attract its armature against its lower contact thereby establishing a circuit for the relay 224 which may be traced from grounded battery through the winding of relay 22%, con due-tor 223 and thence to ground through the armature and lower contact of relay 225. The energization of relay 22 1 connects the source 233 of 135 cycle alternating current to the primary transmitting winding 234: of the circuit 204; over a circuit which may be traced from one terminal ot the source through the inner armature and front contact of relay 22st, conductor 235, primary winding 23%, conductor 236 and thence to the other terminal of source 233 through the outer armature and front contact 01 relay 2341-. Current flowing in this circuit. from the source is of full strength and causes current to flow by induction over the conductors of toll line L to the originating exchange X. The circuit over which this current flows may be traced from the grids of thermionic relays 120 and 121, conductor 122, the upper right-hand coil of the secondary winding 117 of the conjugate circuit 113, tuned circuit 118, conductor 200 of toll line L, tuned circuit 205 at exchange Y, the upper coils of secondary winding 203, balancing network 237, the lower coils of secondary winding 203, tuned circuit 205, conductor 207 ot' the toll line L, tuned circuit 118 at the exchange X, the lower right-hand coil of the secondary winding 117, conduct-or 123 and thence in parallel to the filaments of thermionic relays 120 and 121. It is to be noted that current flowing in the circuit 1 at the exchange Y and impressed thereon from the primary winding 23% has no etteet upon the thermionic relays 201 and 209.

Since current ot tull strength has been transmitted over the toll line from the source 233 both thermionic relays 120 and 121 at the exchange X res 'iond, current therefore lowing in the respective outputcircuits of these relays. The output circuitof thermionic relay 120 may be traced "from the plate of this relay through the condenser 126 and the winding of alternating current relay 1 7 to ground. The output circuit of thermionic relay 121 may be traced from the plate of this relay through the condenser 129 and the winding of alternating current relay 130 to ground. The B battery 125 sup plies constant potential to the plates of relays 120 and 121 through the impedance coils 12 1 and 128 respectively. Both relays 127 and 130 become energized.

The energization of relay 130 closes a circuit for ringing relay 131 which may be traced from grounded battery through the winding of this relay to conductor 132 and thence to ground tlnrough the armature and front contact of relay 130. The operation of relay 131 is without eliect since the circuit leading to the automatic apparatus at eX- change X is open at the alternate contact of relay 134 and. the polarized relay corresponding to relay 225 is not affected by the alternating current impressed upon its windings by relay 131.

Relay 127 upon energizing establishes a shunt around resistance element 110 for the purpose of reducing the resistance of the circuit previously traced through the winding of marginal relay 103. This shunt circuit may be traced from ground at the armature and front contact of relay 127, conductor 135, the armature and front contact of relay 108, which relay is at this time energized over the sleeve circuit extending through the winding of relay 103, and over conductor 130 to the ungrounded terminal of resistance element 110. The current flowing through the winding of narginal relay 103 is now increased to such an extent that the relay energizes, closing a circuit for lighting the supervisory lamp 136 which lamp when lighted at this time signifies to the operator that the connection over the toll line has been cut through to the first selector switch 200 in which the toll line terminates at the distant exchange and that she may now proceed to dial the number of the desired sub- Scriber.

The toll operator now throws the dialing key 102, which at its break contact opens the direct connection from the sleeve conductor to battery and at its make contact substitutes a new connection to battery through the contacts of impulse transmitting mechanism 137. Under the assumption that the number of the desired subscriber B is 256 the toll operator will first operate the impulse transmitting mechanism to transmit two impulses over the toll line. The impulse t 'ansmitting mechanism ma T be of the usual dial t 9e which when rotated from normal in accord ance with any digit which it is desired to transmit and allowed to return to normal will open the impulsing circuit a number of times corresponding to the digit which it is desired to send. In accordance with the setting of the impulse mechanism 137 for the first digit two the sleeve circuit, pre viously traced through the windings of relays 103, 104, 108 and 109, is opened twice iherebv causing two de-energizations of re- 7 lay 100. The relays 108 and 104 do not deenergize upon the momentary interruptions of the circuit through their windings since they are designed to be slow-to-release and therefore the circuits established by the energization of these relays are not disturbed at this time.

Upon each de-energization of impulse relay 109 current from the source 111 is n10- mentarily disconnected. "from the primary winding 112 and theretore current n1omentarily ceases to iiow through the input circuit of the thermionic relay 201 at the distant exchange Y, and in response to each momentary stoppage of current flow in the input circuit of relay 201, relay 213 becomes tie-energized and at its armature and front contact opens the circuits previously traced through the windings of relays 214 and 275. Relay 214 being slow to de-energize does not retract its armatures upon the momentary interruptions of current through its winding but relay 275 becomes deenergized upon each de-energization of relay 213. Upon each de-energization of relay 275 the circuit of line relay 226 01 selector switch 200 is opened and the circuit of primary Stepping magnet 232 is completed from grounded battery through the winding of magnet 232, the winding of slow-to-release relay 237, righthand armature and frontcontact of slow-torelease relay 231, the right-hand armature and back contact of switching relay 228 and thence to ground at the armature and back contact of relay 226. Stepping magnet 232 and slow-to-release relay 237 energize in this circuit and since two impulses are transmitted over the toll line L by the originating operator, the stepping magnet 232 is energized twice to step the switch shaft of the selector switch 200 two steps Vertically to position and wipers 238, 239 and 240 before the second level of bank terminals to which the switch wipers have access. Relay 237 being slow-to-release maintains its armature attracted so long as stepping impulses flow through the winding of stepping magnet 232, and thus maintains an energizing circuit for the test relay 241 which may be traced from grounded battery through the armature and front contact of relay 237 and the winding of test relay 241 to ground. After the switch shaft is moved upwardly one step the oil normal contacts 242 close and establish a locking circuit for the test relay 241 which may be traced from grounded battery through the left-hand armature and front contact of relay 231, conductor 243, the right-hand armature and back contact o'l secondary stepping magnet conductor 245, off normal contacts 242 and thence to ground through the armature and front contact and winding of? relay 241.

Following the transmission oi. the two i111- pulses, relay 109 at the exchange remains energized and the current from source 111 is steadily transmitted over the toll line L and the thermionic relay 201 and relay 275 remain steadily energized to maintain the circuit of line relay 226 closed. Relay 226 now being steadily energized holds open the circuit- PI'QYlOllSlY traced through the wind ing of slow-t0-release relay 237 and the winding of stepping magnet 232 and after an interval relay 237 retracts its armature opening the initial energizing circuit of test relay 2&1 and closing at its armature and back contact an initial energizing circuit for the secondary stepping magnet 2-H. This circuit may be traced from grounded battery through the lett-hand armature and front contact of relay 231, conductor 2 1-3, right-hand armature and back contact of stepping magnet 244, conductor 2&5, oft normal contacts 242, the right-hand armature and front contact of test relay 241, armature and back contact of relay 237, the lefthand armature and back contact of stepping magnet 214 and thence to ground through the winding of stepping magnet 24A. Stepping magnet 2et i energizes in this circuit and advances the switch wipers to the first set of bank terminals in the selected second level. It the trunk line terminating in this first set of bank terminals is busy there will be battery potential upon the testterminal of this trunk and the test relay 241 will therefore be maintained energized even though its locking circuit previously traced through the right-hand armature and back contact of stepping magnet 24a is opened upon the energization of stepping magnet 2 kt. The new locking circuit for test relay 241 may be traced from grounded battery on the test terminal of the busy trunk, test wiper 240, conductor 247. and thence to ground through the right-hand armature and front contact and winding of relay 2-11. Stepping magnet 244 which upon energizing opens its own circuit at its letthand armature and back contact and upon deenergizing, causes the advance of theswitch wipers to the first set of bank terminals. now re-energizes in view 017' the tact that test relay 241 is still locked up, the circuit of magnet extending as previously traced from grounded battery at the le't't-hand armature and tront contact of relay 231. in this manner stepping magnet 2-;1-+t continues to advance the switch wipers over the bank terminals of the second level until the terminals of an idle trunk extending to a connector switch 250 are encountered when the locking circuit of test relay 241 is opened at the right-hand armature and back contact ot stepping magnet 2H to open the circuit of stepping magnet 24%.

Upon the de-energization of test relay 2 11 a. circuit is established for the switching relay 228 which may be traced from grounded battery through the left-hand armature and back contact of relay 241, conductor 245, off normal contacts 24:2 the right-hand armature and back contact of relay 24:1, conductor 2&8 and thence to ground through the winding of relay 228. A branch of this circuit extends from otf normal contacts 242' over conductor 2 27 to test wiper 240 or connecting battery potential to the multiples of test terminal 246 of the engaged trunk to mark this trunk as busy to all other selector switches having access thereto. The energization of switchin relay 228 opens the circuit previously traced through the windings of relay 226 and the windings of polarized relay 225 and extends the trunk conductors 229 and 230 over wipers 238 and 239 and bank terminals 2-3t9 and 251 of selector switch 200 to the windings of line relay 252 of the connector switch 250 and polarized relay and line relay 252 now energize in this circuit. At its right-hand armature and back contact switching relay opens the circuit previously traced through the windings of slow-to-release relay 237 and the primary stepping magnet 232 to prevent the false energization of stepping magnet 232 due to the de-energization of relay 226 when its windings are disassociated from trunk conductors 229 and 230. The circuits at the exchange Y are now in condition to receive the last two digits of the number of the called subscribers line for setting the wipers ot the connector switch 250 upon the terminals of this line.

The current flowing through the windings of line relay 252 of connector switch 251) and through the windings of polarized supervisory relay 225 is still in such a direction as to maintain the armature of pola rized relay attracted against its lowermost contact thereby maintaining current from the source 233, connected over the toll line for continuing the illumination of supervisory lamp 136 at the toll operatous cord circuit. Line relay of the cornicetor switch functions in the well known manner to cause the wipers of the connector switch to be stepped vertically in response to the digit five to the 5th level of bank terminals and then rotated six steps to the 6th set of terminals in this level. Following the transmission ot the digits of the number of the called subscriber, the toll operator restores the dialing key 102 thereby disconnecting the impulse transmitting mechanism 137 from the sleeve conductor of the cord cir cuit. The setting of the wipers ot the connector switch 250 upon the terminals of the desired line and testing ot the line take place in the usual manner.

The operator now proceeds to apply ringiug current to the outgoing terminals of the toll line tor ringing the bell at the substation o't line B by throwing the usual ringing key (not shown) associated with the cord circuit. Ringing current now flows through the winding of ring-down relay 138 which relay becomes energized closing a circuit for relay 139. The circuit of relay 139 may be traced from grounded battery through the winding of relay 139 and thence to ground through the armature and front contact of relay 13,0. Relay 139 upon energizing attracts its armature thereby shunting the resistance element 116 in the circuit extending from the source of current 111 through the primary .vinding 112, whereupon the current flowing through the winding 112 is increased therehy increasing the current flowing through the input circuits of thermionic relays 201 and 209 at the exchange Y. Thermionic relay 209 now receives sufficient current to respond so that current flows in its output circuit from the plate through condenser 254i and alternating current relay Relay 255 upon energizing closes a circuit for ringing relay 256 extending from grounded battery through the winding of relay 256 conductor 257 and thence to ground at the armature and front contact of relay 255. Relay 256 energizes in this circuit and at its armatures and back contacts opens the circuit extending from the incoming end of the toll line through the contacts of relay 27 over condoctors 229 and 230 to the wipers of connector switch 250, and at its armatures and front contacts establishes a circuit which may be traced from the source of ringing current 258, the inner armature and front contact of relay 256, the armature and front contact of relay 275, conductor 230, the innor left-hand armature and front contact of relay 228, wiper 239 and terminal 2 31 of selector switch 200, Wiper 259 and bank 1'81- minal 260 of connector switch 250 thence over the subscribers line and through the bell at the substation thereof and returning through bank terminal 261 and wiper 202 of connector switch 250, terminal 2&9 and wiper 238 of selector switch 200, the outer left-hand. armature and trout contact of ringing relay to ground.

Following the application of ringing current and upon the response of the called subscriber, relay 263 at the connector switch hecomcs energized and by attracting its armatures reverses the battery connections through line relay 252 of the connector switch to the circuit previously traced extending through the windings o'l polarized relay The current now flowing through relay is in such a direction that its armature is attracted against its upper contact thereby opening the circuit of relay 22laud disconnectlug the sour o of current 233 from the primary transmilti g winding 234-. At the origii'iating exchange X the thermionic relays 120 and 121 are now deprived or current in their input circuits and relays 127 and 130 thereupon tie-energize. The de-energization of relay 127 disconnects the shunt previously traced from around re sistance element 110 thereby increasing the resistance of the sleeve circuit extending through the winding of marginal supervisory relay 103 whereupon relay 103 dc-enerto open the circuit of lamp 136 to signal the toll operator that the called subscriber has responded.

The talking circuit extending from the exchange X to the line of subscriber B may be traced over the heavy conductors 1%0, 1 11, 207 and 206 to the exchange Y and thence through armatures and back contacts: of relay 256, conductors 229 and 230 to the line oif the called subscriber, the called subs scriber receiving talking current at the connector switch through the windings of relay 263. Voice currents are allowed to pass freely through the high pass filter 142 at the exchange X and the high pass filter 267 at the exchange Y but due to the tuning of tuned circuits 118 and 205 at the out going and incoming ends of the toll line the voice currents are not transmitted through the circuits 113 and 20 1 respectively.

Upon the termination of the conversation both the calling and the called subscribers restore their receivers to their respective switch hooks. At the exchange X the toll operator is given a disconnect signal upon the restoration of the calling subscribers receiver to its switch hook in the well known manner. Upon the restoration of the called subscribers receiver to its switch hook relay 2623 becomes ale-energized and reconnects hattery through the windings of line relay 252 to the circuit extending through the wind ings of polarized relay 225 in such a manner that the current flowing through the relay 225 now flows in such a direction as to cause this relay to attract its armature nst its lower contact. The circuit of relay 224- is again established and current from the source 233 is again transmitted over the toll line L to the originating exchange where thern'iionic relays 120 and 121 again respond to cause the energization of relays 127 and 130. Relay 127 upon energizing reconnects the shunt around resistance element 110 thereby causing the energization of marginal supervisory relay 103 at the toll operators cord circuit to close the circuit of? supervisory lamp 136.

The toll operator noting the illumination of the supervisory lamps of her cord circuit withdraws the plug P from the jack J thereby opening the circuit previously traced over the sleeve contacts of the plug and ack through the wii'idings ol relays 103, 104i, 108 and 10$) T he de-energization oi? relay 104- opcns the tip strand oi. the cord circuit, the de-energizati on of relay 103 opens the circuit of supervisory lamp 136 and. the de energization Off relay 109 disconnects the source oi? current 111 "from the transmitting circuit including the primary winding 112. Bela-y 108 in releasing reconnects the conductor leading to the automatic switchin apparatus at exchange in preparation for the receipt of a call from exchange Y. Alter- .zitllig current now ceases to .tlow over the toll line from the originating exchange X to the distant exchange Y and relay 213 at the exchange Y is now deprived of current and (re-energizes.

Relay 213 upon de-energizing opens the circuit pre .'iously traced extending through the windings of relays 21s: and 275. Relay upon de-energizing opens the circuit i rcviously traced through windings 0t reaiys 225 and whereupon the connector switch is restored in the well known manner. The de-encrgization of relay 213 at its back contact closes a circuit for restoring the selector switch 200 which may be traced from grounded battery through the winding of release magnet 26iot the selector switch, off normal contacts 265, conductor 266 and thence to ground at the armature and back contact of relay 213. The release magnet 264C, upon energizing, causes the release of the selector switch in the well-known manner, which switch, upon reaching its normal position, opens the ott normal contacts 265 and 242, thereby opening the previously traced circuit through the winding of release magnet Relay 214, upon de-energizing, disconnects battery potential from sleeve 218 or" the jack 5 and opens the circuit previously traced through the drop signal 221, thereby removing the busy condition from the outgoing erminal of the toll line L at the exchange L The apparatus employed in the establishment of the connection is now entirely restored to normal.

The establishment of a connection from the exchange Y over tiie toll line L to theexchange X is attained in exactly the same .uanner as hereinbetore described in connecl iion with the establishment of a connection 1 10111 exchange X to exchange Y, tl e apparatus at the two ends of the toll line being identical and functioning in exactly the same manner on outgoing and incoming calls.

lVhile the invention has been illustrated as operating upon a full mechanical basis at the incoming ends oi the toll lines, it .is to be understood that the selector switches in which the toll lines terminate may equally well extend the toll lines to jacks appearing in manual operators positions so that toll connections might then be extended from the incoming ends of the toll lines semi-automatirally.

Furthermore. the invention is not to be considered as limited to the use of alternating currentof any specified frequency as any suitable frequency of current may be employed.

What is claimed is:

1. In a telephone system an originating exchange, a distant exchange, a subscribers line terminating in said distant exchange, a trunk line extending between said exchanges, automatic switching mechanism at said distant exchange associated with the incoming end of said trunk line for extending a connection from said trunk to said subscribers line, a control circuit for said switching mechanism, av relay for controllin said circuit, a cord circuit at the originating exchange for connection with said trunk line, means operative over the sleeve conductor of said cord circuit upon connection with said trunk line "for causing the application of alternating current to said trunk line for energizing said relay, an impulse transmitting means associated with the sleeve conductor of said cord circuit for thereafter interrupting the application of said current for operating said relay while said cord circuit and said trunk line are interconnected to control said switching mechanism.

2. In a telephone system, an originating exchange, a distant exchange, a. subscribers line terminating in the said distant exchange, a trunk line extending between said exchanges, automatic switching mechanism at the said distant exchange associated with the incoming end of said trunk line for extending a connection from said trunk line to said subscribers line, a control circuit for said switching mechanism, a relay for controlling said circuit, means operative upon the seizure of said trunk line at the originating exchange for applying alternating current to said trunk line for causing the energization of said relay, means at said dist-ant exchange responsive to the energization of said relay for transmitting alternating current from said distant exchange over said trunk line to said originating exchange, and means at said originating exchange responsive to said current for producing a dialing signal.

3. In a telephone system an originating exchange. a distant exchange a subscribers line terminating in said distantcxchange, a trunk line extending between said exchanges, automatic SiitClilIig mechanism said distant exchange associated with the incoming end of said trunl: for extending a connection from said trunk line to said suhscrihers line, a control circuit for said switching mechanism, a relay for controlling said circuit, a cord circuit at said originating exchange tor connection with said trunk line, a supervisory signal associated with said cord circuit, means operative upon connection with said trunk line for applying alternating current to said trunk line for causing the energization of said relay, and means responsive to the energization of said relay for transmitting alternating current over said trunl-z line from said distant exchange to said originating exchange for operating said SUPGL'ViSOlY signal.

4. In a. telephone system an originating exchange, a distant exchange, a subscribers line terminating in said distant exchange, a trunk line extending between said exchanges, automatic switching mechanism at said distant exchange associated with the incoming end of said trunk line for extending a connection from said trunk line to said subscribers line, a control circuit for said switching mechanism, a relay for controlling said circuit, means at said distant exchange for applying ringing current to said subscribers line, means operative upon the seizure of said trunk line at the originating exchange for applying alternating current to said trunk line for causing the energization of said relay, means for thereafter interrupting the applicationof said current for operating said relay to control said switching mechanism, and means at said originating exchange for increasing the strength of said alternating current for operating said ringing current applying means.

5. In a telephone system an originating exchange. a distant exchange, a subscribers line terminating in said distantexchange, a trunk line extending between said exchanges, automatic switching mechanism at said ong inating exchange associated with the incoming end of said trunk line for extending a connection from said trunk line to said subscribers line, a control circuit for said switching mechanism, a relay for controlling said circuit, a cord circuit at said originating exchange for connection with said trunk line, a supervisory signal associated with said cord circuit, means operative upon connection with said trunk line at the originating exchange for applying alternating current to said trunk line for causing the energization of said relay, impulse transmitting means associated with said cord circuit for thereafter interrupting the application of said current for operating said relay for controlling said switching mechanism, and means at said distant exchange responsive to the response of the called subscriber for transmitting alternating current over said trunk line to said originating exchange for controlling said. supervisory signal.

6. In a telephone system, two exchanges, subscribers lines terminating in each of said exchanges, a two-way trunk line extending between said exchanges said trunk line terminating at each exchange in an outgoing terminal and an incoming terminal, said incoming terminal having associated therewith automatic switching mechanism for extending connections to said subscribers lines terminating in the associated exchange, means at each exchange for seizing the outgoing terminal of said trunk line and for thereafter transmitting impulses of alternating current over said trunk line for controlling the switching mechanism at said other exchange, and means at each exchange for simultaneously transmitting impulses of alternating current over said trunk line for supervising the establishment of the connection.

7. In a telephone system an originating exchange, a distant exchange, a trunk line ex ending between said exchanges, said trunk line having two branches at its incoming end, automatic switching mechanism associated with one of said branches, means at said originating exchange for transmitting impulses of alternating current over said trunk line for controlling said switching mechanism and tor controlling supervision of the connection, a filter in one of said branches for attenuating said impulses of alternating current but transmitting current of voice frequency without attenuation, and a tuned circuit in said other branch tuned to respond only to current oi said switch controlling and supervisory frequency.

8. In a telephone system an originating exchange, a distant exchange, a subscribers line terminating at said distant exchange, a trunk line extending between said exchanges having two branches at its outgoing and incoming ends, automatic switching mechanism associated with one branch of said trunk line at said distant exchange for extending connections from said trunk line to said subscribers line, a control circuit for said switching mechanism, a relay for controlling said circuit, a cord circuit at said originating exchange for connection with said trunk line, means operative upon con nection with said trunk line for applying alternating current to said trunk lin for causing the energization of said relay, a supervisory signal associated with said cord circuit, impulse transmitting means associated with said cord circuit for there-after interrupting the application of said current for operating said relay to control said switching mechanism, means at said distant exchange under the control otsaid called subscriber for transmitting alternating current over said trunk line to said originating exchange for controlling said supervisory signal, a filter in one branch of said trunk line at each exchange for attenuating said alternating current but transmitting current of voice frequencies without attenuation, and a tuned circuit in the other branch of said trunk line at each exchange responsive only to said alternating current.

9. In a telephone system an originating exchange. a distant exchange, a subscribers line terminating in said distant exchange, a trunk line extending between said exchanges having two branches at its incoming end, automatic switching mechanism at said distant exchange associated with one branch of said trunk line for extending a connection frcm said trunk line to said subscribers line, a control circuit for said switching mechanism, a relay for controlling said circuit, means at said originating exchange operative upon the seizure of said trunk line for applying alternating current to said trunl: line for causing the energization of relay, means for thereafter inerrupting the application 01 said current for operating said relay to control said switching mechanism, means at said distant exchange for transmitting ringing current to said subscribefis line, a filter in one branch of said trunk line for attenuating said alternating current but transmitting current of voice frequencies without attenuation, a tuned circuit in said other branch responsive only to said alternating current and means at said originating exchange for increasing the strength of said alternating current for operating said ringing current transmitting means.

10. In a telephone system an originating exchange, a distant exchan a subscribers line terminating in said distant exchange, a trunk line extending between said exchanges having two branches at its incoming end, automatic switching mechanism at said distant exchange associated with one branch of said trunk line for extending a connection from said trunk line to said subscribers line, a control circuit for said switching mechanism, a relay for controlling said cir cuit, means at said originating excl'iange operative upon the seizure of said trunk line for applying alternating current to said trunk line for causing the energization of said relay, means for thereafter interrupting the application of said current for operating said relay to control said switching mechanism, means at said distant exchange for transmitting ringing current to said subscribers line, a filter in one branch of said trunk line for attenuating said alternating current but transmitting without attenuation, current of voice frequencies, a tuned circuit in said other branch responsive only to said alternating current, means associated with said tuned circuit responsive to said alternating current of one strength for controlling said relay, a second means associated with said tuned circuit responsive to said alternating current of increased strength for controlling said ringing current transmitting means and means at said originating exchange for increasing the strength of said alternating current.

11. In a telephone system an originating exchange, a distant exchange, a subscribers line terminating in said distant exchange, a trunk line extending between said exchanges having two branches at its incoming end, automatic switching mechanism at said distant' exchange associated with one branch of said trunk line for extending a connection from said trunk line to said suhscribers line, a control circuit for said switching mechanism, a relay for controlling said cir cuit, means at said originating exchange operative upon the seizure of said trunk line for applying alternating current to trunk line for causing the energization ot said relay, means for unereafter interrupting' the application of said current for operating said relay to control said switching mecl1anism, means at said distant exchange for transmitting ringing current to said subscribers line, a filter in one branch oi said trunk line for attenuating said alternating current but transmitting without attenuation, current of voice frequencies, a tuned circuit in said other branch responsive only to said alternating current, a thermionic relay associated with said tuned circuit rcsponsive to said alternating current of one strength for controlling said relay, a second thermionic relay associated with said tuned circuit responsive to said alternating current of increased strength for controlling said ringing current transmitting means and means at said originating exchange for increasing the strength of said alternating current.

12. In a telephone system, an originating exchange, a terminating exchange, a subscribers line terminating in said terminating exchange, a trunk line extending between said exchanges, automatic switching mechanism at said terminating exchange associated with the incoming end of said trunk line for extending a connection from said trunk line to said su'bscribers line, a relay for controlling said switching mechanism. means operative upon the seizure of said trunk line at the originating exchange for applying alternating current to said trunk line "for causing the energization of said relay, means at said originating exchange for interrupting the application of said current for further controlling said relay while said cord circuit and said trunk line are interconnected to cause the operation of such switching mechanism, means at said terminating exchange responsive to the energiza tion of said relay for transmitting alternating current from said terminating exchange over said trunk line to said originating exchange, and means at said originating exchange responsive to said current for producing a dialing signal.

13. In a telephone system, an originating exchange. a terminating exchange, a subscribers line terminating in said terminating exchange, a trunk line extending be tween said exchanges, automatic switching mechani m at said terminating exchange for extending connection from said trunk line to said subscribers line, a control circuit for said: switching mechanism, a relay for controlling said circuit, a cord circuit c t-crating said supervisory signal, and means at the originating exchange for 1nter rupting said alternating current applied to said trunk line hereat while said cord circuit and said trunk line are interconnected to further control said relay for operating said switching mechanism.

it in a telephone system, an originating exchange, a terminating exchange, a sub- :rihers line terminatingin said terminati'o: exchange, a trunk line extending between said exchanges, automatic switching mechanism at said terminating exchange for extending" a connection from said trunk line to said subscribefls line, a control circuit for said switching mechanism, a relay for controlling); said circuit, means at said terminat ing exchange for applying alternating cur rent to said subscribers line, means operative upon the seizure of a trunk line at the originating cxrl'iange for applying alternating: current to said trunk line for causing the cnergr ization of said relay, means for thereafter interrupting the application of said current while said trunk line remains seized for operating said relay to control said switching mechanism, and means at said originating exchange for increasing the strength of said alternating; current for operating; said ringing current applying means.

15. In a telephone system, an ori 'inating exchange, a distant exchange, a subscribers line terminating in said distant exchange, a trunk line extending between said exchanges having two branches at its incominnend. automatic switching mechanism at said distant exchange associated with one branch oi? said trunk line tor extending a connection from said trunk line to said sub- Ihers line. a control circuit for said i/ching' niechanisn'i, a relay for controlling; said circuit, means at said originating); exchange operative upon the seizure of said trunk line for applying alternating current to said trunk line for causing the encrgg ization of said relay, means at said distant exchange for transmitting ringing current to said subscribers line, a filter in one branch of said trunk line for attenuating said alternating current but transmitting); without attenuation currents of voice trequencie, a tuned circuit in said other branch responsive only to said alternating current, means associated with said tuned circuit responsive to said alternating current ct one strength for controlling said relay, second means associated with said tuned eirhi t respoi jve to said alternating cur- 1 increased strength for controlling the ringing: current transmitting meat and means i said originating exchange 'tei' increasing the str ngth of said alternating current.

16. In a telephone system, an ori inatinc exchange, a distant exchange, a su )scribers line t rminating in said distant exchange, a. trunl: line extending between said one changes, means at said distant exchange for interconnecting said trunk line and said subscrihers line, a relay for controlling said interconnecting means, means at said originating" exchange operative upon the seizure of said trunk line for applying; alternating curr (it to said trunk line for energizing: said relay, means at said distant exchange for transmitting ringing cur'ent to said subscrihers line, a tuned circuit at said distant exchange associated with said trunk line responsive to said alternating current, athermionic relay associated with said tuned circuit responsive to said alternating: current oi. one strength for controlling; said relay, a second thermionic relay associated with said tuned circuit responsive to said alternating current of increased strength for controlling said ringing current trans mitting means, and means at said originating exchange for increasing the strength o't said alternating); current.

17. In a telephone system, an originating exchange, a distant. exchange, a subscribers line terminating in said distantexchange, a trunk line extending between said exchanges having two branches at its outgoing and incoming ends, automatic switching mechanism associated with one branch of said trunk line at said distant exchange for extendinp; connections from said trunk line to said suhscribers line, a control circuit for said switching mechanism, a relay for con trollii'ig said circuit, a cord circuit at said originating exchange for connection with said trunk line, means operative upon connection o't said trunk line for applying: alternating current to said trunk line tor causing; the energization ot' said relay, a supervisory signal associated with said cord circuit, impulse transmitting; means associated with said cord circuit tor ap plying: alternating current of another trequeney to said trunk line for controlling the switching' mechanism, means at said distant ext i t ne under the control oi the calling subs her tor t1 insmitting alter ating; current over said trunk line to said originating exchange tor controlling: 'the supervisory si 151i, a filter in one branch of said trunk line at each exchange for attenuating the current of the supervisory frequency but transmitting; Without" attenuation current of tie su'itch controlling frequency, and a tuned circuit in the other branch oi the trunk line at e ch exchange responsive only super A cry frequency.

18 in a telephone exchange s stein, an ing exchange, a distant exchang a s-subscribefis line terminating in said distant exchange, a trunk line er-ltendingbetween said exchanges haying two branches at its incomiu, end, automatic switching mechanism at said distant exchange associated with one bran i-ii of said trunk line for e Ieniing a connection to said subscribers line. control circuit for said switching; li'iOCllEllllSlll, a relay tor controllii'ig said circuit, means at said originating exchange operative upon the seizure of said trunk line for applying alternating current of a certain frequency to said trunk line for energizing said relay, means for applying current of another frequency to said trunk line for also causing; the operation of said relay to control said switching mechanism, means at said distant exchange for transmitting ringing; current to said subscribers line, a iilter in one branch of said trunk line for at tenuating said first mentioned alternating current but transmitting current of the second mentioned frequency Without attenuatien, a timed circuit in said other branch responsive only to said first mentioned alter nating current, and means at said originating exchange for increasing the strength of said alternating current for operating said ringing current transmitting neans.

19. A transmission circuit, a plurz' thermionic devices having input circles con-- nected to said transmission circuit and hav ing separated output circuits, an elei iit associated with each of said output circuits, a source oi current, switching means for impressing current lroii'i said source upon said transmission circuit to operate one o'l'j said devices and thereby control the associated element, and additional switching means for increasing tie intensity of current from said source to operat a plu rality of said devices and thereby control the associated elements.

20. A transmission circuit, a plurality of thermionic devices connected to said trans-- mission circuit, a source of current, switching means for connecting said source to said transmission circuit to operate a plurality of said thermionic devices and regulating means to vary the intensity of the current from said source to operate one of said thermionic devices singly.

A transmission circuit, means for supplying currents of difierent intensity thereto, and plurality of thermionic devices sociated With said circuit and selectively operable by said currents.

In testimony whereof, I have signed my name to this specification this 15th day of December 1920.

JOHN F. TOOMEY.

y o t 

